Problem: Rewrite ${\dfrac{9^{9}}{9^{-11}}}$ in the form ${9^n}$.
Explanation: ${ \dfrac{9^{9}}{9^{-11}} = 9^{9-(-11)}} $ ${ \hphantom{\dfrac{9^{9}}{9^{-11}}} = 9^{20}} $